A number of solid granular materials commonly are pumped in slurry form. For example, sand, mill tailings, coal, and aggregates can be transported through a pipeline in a sufficiently large volume of water. For example, when it is desired to transport mill tailings, such tailings are dumped into a cone-bottom tank. There they are mixed with a liberal quantity of water and pumped through a pipeline to a settling pond. However, upon arrival at the pond, the tailings quickly settle out of the water and form mounds that must be leveled by additional efforts.
If such tailings or other solids are being used to backfill mine areas or underground voids, their tendency to settle out of the carrier water presents a problem. The uneven settling of the solids leaves unfilled areas, and it is difficult or impossible to redistribute them uniformly.
The transportation of solids in pipelines has been attempted by a number of processes. The basic concept has been to suspend the solids in a sufficient quantity of liquid to sweep the solid with the flow of the liquid. However, this technique is unsatisfactory when the liquid is scarce or valuable, difficult to recover, or difficult to dispose of. Similarly, the use of substantial quantities of liquid in a pipeline is unsatisfactory when it becomes costly or difficult to recover the solid in the desired, useable condition. Another problem is that solids may tend to settle out of the carrier liquid if velocity is sufficiently low. A number of transportation techniques have been proposed to overcome these problems.
Scott U.S. Pat. No. 3,206,256 proposes to overcome the tendency of particles to settle out in the pipeline by agglomerating the particles with an immiscible film, bringing the density of the agglomerate closer to the density of the carrier liquid. This technique continues to employ a substantial quantity of carrier liquid, which is preferred to be a petroleum product. Thus, the patent anticipates the availability of substantial quantities of such liquid, from which the solid must be separated and recovered at the point of destination.
Lissant U.S. Pat. No. 3,617,095 proposes to transport coal and other minerals in pseudo-plastic fluids such as polymer solvents, gels and emulsions. These carrier liquids are said to behave in non-Newtonian fashion, in that effective viscosity varies with rate of shear. This category of carrier liquid does not include water, which behaves in Newtonian fashion in that effective viscosity does not vary with rate of shear. A substantial quantity of carrier liquid continues to be required and must be separated at the point of destination.
U.S. Pat. No. 3,950,034 to Dreher et al. discloses a specially formulated liquid composition for carrying suspended solids. The liquid is a combination of water, hydrocarbon, and surfactant. The carrier liquid exhibits retro-viscous behavior in that it exhibits a large increase in flow rate in response to a small increase in pressure. A substantial quantity of the carrier liquid is required, with preferred solids content being 30% to 50% by weight. Thus, a separation and recovery procedure is necessary at point of destination.
Lorenz U.S. Pat. No. 4,451,183 discloses a method of transporting aggregate by the separate introduction of a foam into a pipeline with the aggregate slurry and moving the foam under pressure. The foam is of types known in the oil industry and is injected at low points in the pipeline, where fines normally tend to settle out from the foam based slurry. Lorenz further proposes to substitute foam for liquid, injecting the foam at the beginning the the pipeline. In this case the foam is regenerated by agitation from an injected gas at various points along the pipeline, and additional foam is injected at low points of vertical runs in the pipeline to prevent the aggregate from falling back. Thus, this process relies upon the high viscosity of the foam to carry the aggregate and upon maintenance of sufficient velocity in the pipeline to keep the aggregate carried by the foam, remixing by adding supplemental gas or foam at the locations where settling-out is most likely.
Various patents have taught the use of foams for fracturing well formations. These foams have included sand or other granular solids as proppants. U.S. Pat. No. 3,980,136 to Plummer et al. discloses such a foam fracturing technique, in which sand, water, and surfactant are mixed and then converted into a foam by injection of a suitable gas. U.S. Pat. No. 3,937,283 to Blauer et al. is of similar content. Thus, the production of foams is well known
It would be desirable to have the ability to move low water content granular solids or aggregates for long distances through pipelines without the requirement of maintaining a high velocity for preventing settling out of the solids.
Similarly, it would be desirable to use existing pipelines for flowing such solids, without requiring special vertical stations for the regeneration of the foam and to pick-up settled out solids.
Also, it would be desirable to produce mixtures of solids and foam that can be moved through pipelines with low friction or resistance.
It also would be desirable to create a self-leveling pumpable material, such that mines could be back-filled and voids filled without leaving empty areas.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the foam product and method of transportation of this invention may comprise the following.